TRACHEATA 347 
with the end of her abdomen, and depositing an egg at each 
dip, or in other species she deposits the eggs on submerged 
water-plants. 
The larvae are very voracious, and feed upon other insects, 
their lower lip or labium is peculiarly modified into a structure 
known as the “ mask,” this can be suddenly shot out, and serves 
to capture food. The larva of Agrion has at the end of its 
abdomen three leaf-like gills, but other species breathe by their 
rectum, the walls of which are richly supplied with tracheae. 
The entrance and exit of the water is controlled by three valves, 
which can be opened or closed at will; in some species the 
sudden expulsion of water serves to propel the larva through 
the water. This anal respiration recalls a similar change of 
function of the posterior part of the alimentary canal in some 
Crustacea (see p. 268). The pupa stage, which precedes the 
- Imago, is in the Libellulidae an active stage, and is sometimes 
termed the “nymph” (Fig, 196). 
Family 5. MyRMELEONTIDAE.—The ant-lion, Myrmeleo, in 
the imago condition has clubbed antennae, a small prothorax, 
a large mesothorax, 
and wings of equal 
size. The larvae live 
at the bottom of 
little conical sandy 
pits, which they ex- 
cavate ; they lie par- 
tially embedded in 
the sand at the bot- 
tom of the pit, and 
seize with their powerful mandibles any insect, ete., which 
happens to stray over the edge. The mouth is closed, 
and the food is sucked in through perforations in the 
mandibles. It is stated that the proctodaeum of the larva 
does not open into the alimentary canal, but is modified to 
form a silk gland, which serves for the spinning of the cocoon 
in which the pupa envelops itself. 
Family 6. In the Family Hemeropupae the larvae of 
Chrysopa and Hemerobius, which are known as Aphis lions, feed 
on Aphides. They also have the proctodaeum modified to form 
Fic. 197.—Ant-lion, Myrmeleon formicarius. 
